[Toybox] _GNU_SOURCE definition problem

[Rob Landley]

On 03/09/2012 04:39 PM, Georgi Chorbadzhiyski wrote:
> On 3/9/12 7:47 PM, Rob Landley wrote:
>> On 03/09/2012 08:14 AM, Georgi Chorbadzhiyski wrote:
>>> Removing _GNU_SOURCE breaks toys/unshare compilation.
>>
>> Building under what?
>>
>> In /usr/include/features.h:
>>
>> #if defined _BSD_SOURCE || defined _SVID_SOURCE
>> # define __USE_MISC     1
>> #endif
>>
>> sched.h includes bits/sched.h, and in /usr/include/bits/sched.h the
>> CLONE_NEW* defines are all in #ifdef __USE_MISC
>>
>> So... works for me?  (Just did a test build...)
> 
> From /usr/include/bits/sched.h [1] on my desktop (glibc-2.14.1,
> slack-current)
> 
> #ifdef __USE_GNU

That's the double underscore macro, that's #defined internally by
/usr/incldue/features.h in response to some other macro.

> ...
> # define CLONE_NEWUTS   0x04000000      /* New utsname group.  */
> # define CLONE_NEWIPC   0x08000000      /* New ipcs.  */
> # define CLONE_NEWUSER  0x10000000      /* New user namespace.  */
> # define CLONE_NEWPID   0x20000000      /* New pid namespace.  */
> # define CLONE_NEWNET   0x40000000      /* New network namespace.  */
> # define CLONE_IO       0x80000000      /* Clone I/O context.  */
> ...

I can #include linux/sched.h directly if this is really a problem.
That's the more correct thing to do since this is a recently added linux
kernel feature, and has nothing to do with gnu anything.

> #endif
> 
> ...
> 
> #ifdef __USE_GNU
> /* Clone current process.  */
> extern int clone (int (*__fn) (void *__arg), void *__child_stack,
>                   int __flags, void *__arg, ...) __THROW;

Hang on, you don't get _clone_ unless you say _USE_GNU?  I get it if I
don't specify _any_ feature test macro.

Something is very broken here.

> Resulting in:
> 
> toys/unshare.c: In function ‘unshare_main’:
> toys/unshare.c:32:20: error: ‘CLONE_NEWNS’ undeclared (first use in this
> function)
> toys/unshare.c:32:20: note: each undeclared identifier is reported only
> once for each function it appears in
> toys/unshare.c:32:33: error: ‘CLONE_NEWUTS’ undeclared (first use in
> this function)
> toys/unshare.c:32:47: error: ‘CLONE_NEWIPC’ undeclared (first use in
> this function)
> toys/unshare.c:32:61: error: ‘CLONE_NEWNET’ undeclared (first use in
> this function)
> toys/unshare.c:40:2: warning: implicit declaration of function ‘unshare’
> [-Wimplicit-function-declaration]
> make: *** [toybox] Error 1
> 
> glibc insists that this Linux only functionality is behind __USE_GNU
> which is declared in features.h if _GNU_SOURCE is declared [2].

glibc 2.11.1 here does not, sounds like a recent regression.

But sure, I can #include linux/sched.h to get this.

Rob